What are the purple marks on Michael Phelps?

If you watched the incredible proof swimming what happened on Sunday, with the victory of the US team in the 4x100 relay, you may well have paid attention to Michael Phelps.

Some people noticed that he had some purple marks on the skin and questioned what they would be.Not only Michael, but other athletes exhibit such spots, the result of an ancient practice of Chinese healing called cupping therapy.

Through this technique, beakers are heated and placed on the skin. Thus, when the air inside is cooled, it generates a vacuum which causes suction of the skin, as well as a suction cup.

At that time, the skin moves away slightly from the underlying muscles, leaving the marks you can see in the picture.

It's the same thing that happens when someone takes a "hickey" on her neck.